This lynda.com course is a must-see for anyone shooting documentaries. It includes invaluable information about how to light, stage. and film an interview.
Composition and Camera Motion
Although you will be capturing real events unfolding in real time, you can still be creative about how you compose your shots. See the links below for more information about the techniques of composition and camera motion.
In documentary filmmaking, A-Roll is generally your interview footage, while B-roll is the supporting footage inserted between the interview clips. Some types of documentaries (poetic, observational) do not have this structure and consist entirely of A-Roll footage.